This invention relates to devices for determining contaminants in gases and, more particularly, to a new and useful electrochemical cell for determining the amount of carbon monoxide present in a gas.
Carbon monoxide is a noxious substance which is produced in every combustion of fuels containing carbon, be it in open flame (domestic fuel) or in the cylinder of an internal combustion engine. In addition, emission sources include production processes in commercial plants, such as, for example, blast and cupola furnaces in the steel making industry. Carbon monoxide thus appears in the air of cities and at work places in concentrations having great fluctuations.
There are numerous reports on the noxious effect of carbon monoxide on the human organism; see, for example, G. Malorny in "Staub-Reinhaltung der Luft", Vol. 32, pages 131- 142 (1972 ). In this paper are indicated maximum immission concentrations for carbon monoxide: 8 ppm for 24 h; 16 ppm for 8 h and 80 ppm for h.
The toxicity of carbon monoxide makes it necessary to detect both its emission and its distribution in the environment, and to measure its concentration at points at which persons are endangered, such as, for example, in large cities at heavily congested traffic intersections, in tunnels and in parking spaces, and also a work places in factories, mines, etc.
For the quantitative determination of carbon monoxide, there is a great number of methods, see for example THOENES in "Staub-Reinhalting der Luft", Vol. 32, pages 46- 49 (1972 ). Beside methods using direct chemical reaction (ORSAT principle), the determination by means of gas chromatography and infrared absorption has been very much developed and many firms offer sophisticated apparatus for the continuous determination of the carbon monoxide content. These known devices are, however, utilizable only in stationary locations, because of the size and the weight of the instruments and the dependence on an electric supply line. In this sense, also the special determination installations mounted on vehicles are considered as stationary. Single measurements can also be conducted by means of known carbon monoxide visual detection tubes (K. Grosskopf, "Angew. Chemie", Vol. 63, pages 306 - 308, 1962) in the emission and also in the immission range. The necessary time is small and less than 1 minute is necessary for a determination. The disadvantage, however, is the discontinuity of operation.
There is a known electrochemical apparatus for determination of carbon monoxide concentration (H. W. Bay et al, "International Laboratory", September, October 1972, pages 37- 41 ). The cell of this apparatus, which is an electrochemical half-cell, consists of a measuring electrode, a reference electrode and a counterelectrode. The potential of the measuring electrode is measured in respect to the reference electrode and it is regulated to an adjustable value by means of an electronic potentiostat (instrument for maintaining constant a predetermined electrode potential). At this potential, the carbon monoxide is oxidized electrochemically at the measuring electrode, with release of electrons, and the strength of the current is a measure for the carbon monoxide content of the gas being analyzed. The necessary current supply for the potentiostat and for a gas pump is derived from an accumulator. The neccesity of a reference electrode and of on electronic potentiostat with the respective current supply renders the apparatus expensive and susceptible to troubles. Besides, the accuracy and the reproducibility of the results of determinations are impaired by the continuous water vapor exchange between the electrolyte and the air flowing past.